The invention relates to fringe field switching mode liquid crystal displays (FFS-LCDs), and more particularly, to FFS-LCD electrode array structures.
Generally, liquid crystal displays (LCDs) control light transmittance using an electrical field to display an image. In order to attain this end, LCDs include a liquid crystal panel having liquid crystal cells arranged in a matrix, and a driving circuit for driving the liquid crystal panel.
A common type of technology used in LCDs is a conventional twisted nematic (TN) display. Conventional TN displays, however, have intrinsic properties of narrow viewing characteristics and slow response time. Most particularly, TN displays have slow response time for gray scale operation.
In order to overcome these limitations, various techniques to enhance viewing angle have been suggested. One such technique is an in-plane switching mode liquid crystal display (IPS-LCD). FIG. 1 is a sectional view of a conventional IPS-LCD. In the conventional IPS-LCD, a pixel electrode 110 and a common electrode 120 are formed on a lower substrate (array substrate) 100 and a horizontal electrical field is generated therebetween to rearrange the liquid crystal molecules along the horizontal electrical field. Because the spacing between the pixel electrode 110 and the common electrode 120 is greater than the cell gap between lower and upper substrates 100 and 105, the liquid crystal molecules above the electrodes 110 and 120 cannot display due to the horizontal electrical field, causing a low aperture issue. Moreover, the pixel and common electrodes 110 and 120 comprise an opaque metal material, such as aluminum that is disposed on a transmissive region, thereby further decreasing the LCD aperture ratio.
In order to overcome the low aperture problem of the conventional IPS-LCDs, an FFS-LCD shown in FIG. 2A has been proposed. In the FFS-LCD, a transparent pixel electrode 210 and a transparent common electrode 220 are formed on a lower substrate 200 opposite an upper substrate 205. A distance “L′” between the pixel and common electrodes 210 and 220, respectfully, is thinner than a width “W” of an electrode and a cell gap between two substrates 200 and 205. The horizontal electrical field is thus uniformly distributed between and above the electrodes 210 and 220 thus increasing the aperture ratio of the IPS-LCD. U.S. Pat. No. 6,466,290 to Kim et al., the entirety of which is hereby incorporated by reference, describes an FFS-LCD. U.S. Pat. No. 6,522,380 to Lee et al., the entirety of which is hereby incorporated by reference, describes an LCD with a high aperture ratio.
In the conventional FFS-LCD, the rectangular or straight electrodes 210 and 220, shown in FIG. 2B, are used to produce the fringe field therebetween. This electrode array structure, however, requires the FFS-LCD to have a relatively high operating voltage (>6Vrms) and a liquid crystal material comprising negative dielectric anisotropic (Δε<0) liquid crystals. The negative type liquid crystals are difficult to produce and have a higher viscosity. Thus, an FFS-LCD with an improved electrode array structure is desirable.